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Aanandi took two test tubes and marked them A and B. She put two spoonfuls of sugar solution in each of the test tubes. In test tube B, she added a spoonful of yeast. Then she attached two incompletely inflated balloons to the mouth of each test tube. She kept the set-up in a warm place, away from sunlight.
(i) What do you predict will happen after 3–4 hours? She observed that the balloon attached to test tube B was inflated. What can be a possible explanation for this?
(a) Water evaporated in test tube B and filled the balloon with the water vapour.
(b) The warm atmosphere expanded the air inside the test tube B, which inflated the balloon.
(c) Yeast produced a gas inside the test tube B which inflated the balloon.
(d) Sugar reacted with warm air, which produced gas, eventually inflating the balloon.
(ii) She took another test tube, 1/4 filled with lime water. She removed the balloon from test tube B in such a manner that the gas inside the balloon did not escape. She attached the balloon to the test tube with lime water and shook it well. What do you think she wants to find out?
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Explanation
- (i) Yeast feeds on the sugar and releases carbon dioxide gas, which inflates balloon B. So the answer is (c).
- (ii) Carbon dioxide turns lime water milky.
- By shaking the balloon's gas with lime water, she checks if it turns milky.
- This tells her whether the gas made by the yeast is carbon dioxide.
